全文获取类型
收费全文 | 2578篇 |
免费 | 81篇 |
国内免费 | 15篇 |
专业分类
化学 | 1600篇 |
晶体学 | 10篇 |
力学 | 133篇 |
数学 | 380篇 |
物理学 | 551篇 |
出版年
2022年 | 47篇 |
2021年 | 61篇 |
2020年 | 45篇 |
2019年 | 53篇 |
2018年 | 52篇 |
2017年 | 41篇 |
2016年 | 77篇 |
2015年 | 70篇 |
2014年 | 82篇 |
2013年 | 123篇 |
2012年 | 105篇 |
2011年 | 129篇 |
2010年 | 74篇 |
2009年 | 75篇 |
2008年 | 113篇 |
2007年 | 113篇 |
2006年 | 90篇 |
2005年 | 88篇 |
2004年 | 75篇 |
2003年 | 69篇 |
2002年 | 61篇 |
2001年 | 39篇 |
2000年 | 40篇 |
1999年 | 33篇 |
1998年 | 33篇 |
1997年 | 23篇 |
1996年 | 35篇 |
1995年 | 28篇 |
1994年 | 38篇 |
1993年 | 34篇 |
1992年 | 29篇 |
1991年 | 29篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 37篇 |
1986年 | 30篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1979年 | 28篇 |
1977年 | 26篇 |
1976年 | 38篇 |
1975年 | 26篇 |
1974年 | 23篇 |
1973年 | 23篇 |
1972年 | 22篇 |
1970年 | 21篇 |
1969年 | 20篇 |
1968年 | 21篇 |
1967年 | 25篇 |
排序方式: 共有2674条查询结果,搜索用时 687 毫秒
1.
A protocol to correct for intra‐ and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line 下载免费PDF全文
2.
3.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
4.
The development of a tool for calculating resonances and bound states in three-body systems described by a single-potential
energy surface is reported. The method has been applied to the antiprotonic helium, doubly excited states in helium, the 11Li nuclear halo, the NeICl van der Waals molecule, and the recently found FHD reaction complex.
Received November 26, 2001; accepted for publication November 28, 2001 相似文献
5.
6.
Xiaojuan Hao Camilla Nilsson Martin Jesberger Martina H. Stenzel Eva Malmstrm Thomas P. Davis Emma
stmark Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(23):5877-5890
The synthesis and characterization of novel first‐ and second‐generation true dendritic reversible addition–fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3‐benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z‐group architecture based on 1,1,1‐hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free‐radical polymerization at 60 °C. The novel dendrimer‐based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number‐average molecular weight (Mn) with the monomer–polymer conversion, yielding star polymers with molecular weights of up to Mn = 160,000 g mol?1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol?1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1‐hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star‐shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star‐shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877–5890, 2004 相似文献
7.
Asaf Levin 《Operations Research Letters》2004,32(6):530-534
Consider the following problem: given a ground set and two minimization objectives of the same type find a subset from a given subset-class that minimizes the first objective subject to a budget constraint on the second objective. Using Megiddo's parametric method we improve an earlier weakly polynomial time algorithm. 相似文献
8.
9.
10.